The present invention relates to a liquid discharging head which discharges liquid in a liquid chamber from a nozzle using energy such as thermal energy, a liquid discharging apparatus having the liquid discharging head, and a driving method for the liquid discharging head.
Recently, in the fields of hard copy, printing, and so on, the need for color output has increased. In response to this need, apparatuses have been proposed such as image producing apparatuses and liquid discharging apparatuses using color image production methods such as a thermal dye sublimation method; a thermal wax transfer method; an ink-jet method; an electro-photographic method; and a thermal silver-salt development method.
A liquid discharging apparatus using the ink-jet method discharges a drop of recording liquid (ink) from a nozzle of a printer head, which is a liquid discharging head, onto a recording medium to form a dot. The apparatus has a simple structure and can produce a high quality image. In this ink-jet method, an energy generating element applies energy to the ink in a liquid chamber, thereby causing an ink drop to be discharged from the nozzle. The ink-jet methods are classified according to the kind of energy generating element into an electrostatic attraction type; a continuous-vibration generating type (piezo type); and a thermal type.
In the thermal type, a heater element is used as the energy generating element. Local heating (application of energy) of the ink in the liquid chamber by the heater element generates bubbles in the ink in the liquid chamber. The pressure generated in the bubbles causes the ink to be discharged from the nozzle onto the recording medium. An apparatus using the thermal-type ink-jet method has a simple structure and can print a color image.
A liquid discharging head used in a liquid discharging apparatus using the thermal-type ink-jet method is manufactured by providing a semiconductor substrate with drive circuits, which are logic ICs, driving heater elements; heater elements; ink chambers; and nozzles, in this order, as disclosed in Japanese Unexamined Patent Application Publication No. 7-68759. Since the heater elements are integrated with the drive circuits, the heater elements can be arranged at a high density. Therefore, high-resolution prints can be obtained.
In most of such liquid discharging heads, a head chip having the following structure is used. That is to say, each nozzle is provided with a heater element; the heater elements are aligned in a row on the substrate; on one side of the row, the drive circuits are provided; and on the other side thereof, an ink flow path is provided. By using such a head chip, the liquid discharging head can be miniaturized.
Concerning such a liquid discharging head, as disclosed in Japanese Unexamined Patent Application Publication No. 8-48034, a method for controlling the discharging direction of the liquid drop is proposed. In the method, the discharging direction of the liquid drop is controlled by separately driving a plurality of energy-generating elements provided for each liquid chamber.
FIG. 1 shows the liquid discharging head viewed from the side where the nozzles are provided. In FIG. 1, a nozzle 1 is provided for each ink chamber 2. For each ink chamber 2, two heater elements 3A and 3B are provided side by side in the direction in which the ink chambers 2 are aligned. As shown in FIG. 2, one end of each of the heater elements 3A and 3B is connected to a common wiring pattern 4. The heater elements 3A and 3B are connected to a power supply 5 via the common wiring pattern 4. The other ends of each of the heater elements 3A and 3B are respectively connected to transistors 7A and 7B via wiring patterns 6A and 6B, respectively. The heater elements 3A and 3B are grounded via the transistors 7A and 7B, respectively. The transistors 7A and 7B are separately switched on at a predetermined timing according to the timing-control of a control circuit 9 to drive the heater elements 3A and 3B, respectively. The currents IA and IB flowing through the heater elements 3A and 3B, respectively, are controlled based on the determination of gate-voltage in the on-state by the control circuit 9. The heater elements 3A and 3B have about the same shapes and about the same resistance values. The heater elements 3A and 3B are arranged about symmetrically with respect to the center line of the nozzle 1. The liquid chamber 2 is about symmetrical with respect to the middle line between the heater elements 3A and 3B.
When either heater element 3A or 3B is driven, an ink drop is discharged at an angle.
Concerning the above-described structure, in the case where each nozzle 1 is provided with two heater elements 3A and 3B, where the heater elements 3A and 3B are aligned in a row, where the drive circuits are provided on one side of the row, and where an ink flow path is provided on the other side thereof, however, the wiring pattern 4 or the wiring patterns 6A and 6B connected to the heater elements 3A and 3B need to be bent. In this case, as shown in FIG. 1, a drive circuit composed of the transistors 7A and 7B and the control circuit 9 are provided on the side of the wiring patterns 6A and 6B connecting the heater elements 3A and 3B to the transistors 7A and 7B, respectively. The common wiring pattern 4 is bent and led to the side of the wiring patterns 6A and 6B through the gap between the adjacent heater-element pairs. In this way, the drive circuit and the wiring patterns 4, 6A, and 6B can be laid out efficiently.
The current IA or IB flowing through the individual wiring pattern 6A or 6B, respectively, flows through the common wiring pattern 4. When the transistors 7A and 7B are both driven to drive both of the heater elements 3A and 3B, the current IA+IB flows through the common wiring pattern 4. Therefore, in the conventional structure, the width of this common wiring pattern 4 needs to be greater than or equal to the sum of the width of the individual wiring pattern 6A and the width of the individual wiring pattern 6B. This causes problems in that the nozzles cannot be arranged at a high density. Incidentally, in the conventional structure, if the width of the common wiring pattern 4 is less than the sum of the width of the individual wiring pattern 6A and the width of the individual wiring pattern 6B, wire breakage occurs due to electromigration.